An electroporator uses a high-voltage electrical discharge to introduce cloned DNA into mammalian and any other cells. This method, commonly referred to as transfection, involves creating a suspension of cells in a phosphate-buffered saline (PBS) solution and adding cloned DNA. The suspension is then subjected to a high-voltage pulse from an electrical pulse generator which causes the cells to take up and express the exogenous DNA.
The amount of voltage and current required in transfection procedures depends upon the cell and DNA types, and the electrical characteristics which must be closely controlled. It has been discovered that some transfection procedures require currents of as much as 125 amps and more.
A transfection high-voltage controller is taught by Charles W. Ragsdale in U.S. Pat. No. 4,750,100. FIG. 1 of the Ragsdale patent illustrates a schematic diagram of the circuit used by Ragsdale to deliver a high-voltage pulse to a load such as a cuvette. An AC power supply is coupled to a transformer 52 through an AC switch 28 controlled by a control processor 20. A capacitor 60 is used to store the charge delivered from the transformer 52. This capacitor 60 is allowed to charge to a voltage level above the voltage level requested by a user. After the capacitor 60 has reached a voltage level sufficiently above the requested voltage, the control processor 20 will open the AC switch and the capacitor 60 gradually discharges through the resistor 61. When the charge on the capacitor 60 reaches the requested voltage level the Hi-Joule switch 16 is triggered to pass the charge on the capacitor 60 to the load 74. The Hi-Joule switch 16 is comprised of one or more semiconductor controlled rectifiers (SCR).
The transfection high-voltage controller taught by Ragsdale requires that the capacitor 60, which is used to store and deliver the charge, be overcharged. Once the capacitor 60 is overcharged sufficiently, this charge is bled off through the resistor 61, until the charge on the capacitor 60 reaches the specified level, at which time the switch 16 is triggered and the charge on the capacitor 60 is delivered to the load 74. By overcharging the capacitor 60 and then bleeding off the excess charge, the transfection high-voltage controller taught by Ragsdale is both inefficient and slow.